Locusts have fascinated researchers for several decades, because they have the remarkable ability to undergo phase transition from the harmless solitary to the swarm-forming gregarious phase. However, the physiological and endocrine mechanisms, underlying phase polymorphism, are only partially unravelled. Nevertheless, besides the 'classical' hormones, pacifastin-related peptides have been suggested to play a role in phase transition. Here, we present the first quantitative and comparative analysis of locust transcripts, in particular pacifastin-related precursor (SGPP-1-3) mRNAs, between isolated-reared (solitary) and crowd-reared (gregarious) desert locusts, revealing a phase-dependent transcriptional regulation of the corresponding genes. While the SGPP-1 and SGPP-3 transcripts were most abundant in fat body from crowd-reared males, corresponding to significantly higher levels than in isolated-reared males, the SGPP-2 transcript was detected most abundantly in brain from crowd-reared male locusts. Furthermore, SGPP-2 transcript levels in brain, testes, fat body, and accessory glands from crowd-reared males significantly exceeded the levels in solitary locusts. (C) 2004 Elsevier Inc. All rights reserved.